A loudspeaker is a device for converting electrical signals or impulses into sound. A typical loudspeaker includes a coil of wire wrapped around a piston that is surrounded by a fixed permanent magnet. When a varying electrical signal is applied to the coil of wire, the piston moves axially, typically front-to-back relative to the loudspeaker, within the permanent magnet. A speaker cone (diaphragm) is attached to and moves with the piston. Movement of the cone produces sound according to the frequency and amplitude of the applied current.
Different sizes and configurations of loudspeakers are used to achieve different efficiency levels (sound power output relative to driving electrical power input), frequency response, and speaker size. The specific characteristics of a given loudspeaker often are selected based the expected use of the speaker. For example, in a public address loudspeaker a relatively low distortion at high sound pressure level (SPL) may be required, whereas a relatively poor frequency response may be acceptable. Other configurations and characteristics may be more suited for other applications and locations.